The present invention relates to a process for producing aromatic amines by reduction of aromatic nitro compounds.
Aromatic amines including aniline are industrially important compounds used as medicines, agricultural chemicals, dyes, pigments, pharmaceuticals and intermediates thereof.
It is known to produce aromatic amines by reduction of aromatic nitro compounds under a CO/H.sub.2 O system in the presence of a catalyst. U.S. Pat. No. 3,944,615 discloses to carry out the reaction in a solvent such as pyridine or N-methylpyridine using Rh.sub.6 (CO).sub.16 or Rh.sub.2 O.sub.3 as a catalyst under high temperature and high pressure e.g. 50.degree.-150.degree. C. and CO 50-120 atm. European Patent Laid-Open Application No. 97592 discloses to carry out the reaction in a solvent such as ethanol using Rh.sub.6 (CO).sub.16 as a catalyst with addition of 3,4,5,6,7,8-hexamethylphenanthroline under high temperature and high pressure e.g. 165.degree. C. and CO 30 atm. As a reaction at high temperature (e.g., 80.degree. C.) and under atmospheric pressure, "Journal of Molecular Catalysis", Vol. 12, No. 385 (1981) discloses to carry out the reaction in a solvent of 2-ethoxyethanol-water using Rh.sub.6 (CO).sub.16 as a catalyst with addition of various amines. As a reaction under room temperature and atmospheric pressure, "Tetrahedron Letters", Vol. 21, No. 27, 2603-2604 (1980) discloses to carry out the reaction in a mixed solution of 2-methoxyethanol-benzene-aqueous sodium hydroxide solution using a catalyst Ru.sub.3 (CO).sub.12 and a phase-transfer catalyst such as (PhCH.sub.2)Et.sub.3 N.sup.+ Cl.sup.-.
However, according to these methods, since catalytic activities are low and the reduction is difficult to proceed under moderate conditions, it is necessary to raise reaction temperature or enhance CO pressure. Furthermore, there is a problem in selectivity of reaction products under conditions of high temperature and high pressure. Under the moderate conditions of room temperature and atmospheric pressure, since catalytic activity is low, desired compounds are hardly obtained in high yields unless catalyst concentration is increased or reaction is conducted for a long time even with addition of phase-transfer catalysts.